The invention relates to the repair of building foundations by underpinning. More specifically, it relates to a method for aligning pile segments during installation and continuously reinforcing an improved segmental precast concrete pile used for underpinning repairs.
There is a type of precast concrete pile used in the underpinning of building foundations comprised of vertically stacked, unconnected, precast concrete segments. These segments are pressed or driven vertically into the soil one at a time until adequate load capacity is obtained. This type of pile is distinctive in that it can be installed with almost no clearance, usually beneath an existing structure.
Although serviceable, this pile has several significant disadvantages: (a) the pile segments are not aligned, other than being stacked on each other, and detrimental misalignments can occur, (b) independent inspection of the installed pile depth is only possible by providing full-time inspection personnel during installation to monitor the quantity of pile segments used at each pile location, and (c) the complete pile is an unreinforced stack of precast concrete segments.
Misalignment of the segments as they are installed can produce several conditions detrimental to the future pile stability. Lack of proper independent inspection of pile depth can lead to inadequate pile penetration, which in highly expansive soils produces an unstable installation subject to continued movements caused by seasonal change in soil moisture. An unreinforced or non-continuously reinforced pile is subject to permanent separation at segment joints or breakage at segment midpoints when installed in clay soils having high shrink-swell potentials.
This separation of segments occurs when clay soils swell due to an increase in moisture content. This soil expansion exposes the pile to tension forces. This is especially detrimental to an unreinforced pile because even slight soil intrusion into the gaps between segments prevents closing of the gaps when soil moisture decreases. Over a period of years, this cyclical shrink-swell effect can lift the upper portion of the pile and the unsupported structure. This lifting effect at pile support locations falsely appears as settlement of adjacent unsupported areas.
Various patents have issued on the process relating to the installation of underpinning piles below a structure. U.S. Pat. No. 5,288,175, issued on Feb. 22, 1994, to D. W. Knight, teaches a segmental precast concrete underpinning pile which uses a method of installation where a high strength strand aligns the precast segments during installation and continuously reinforces the pile when bonded or anchored upon completion. The process of this patent includes the driving of a first pile segment into the earth a desired distance from the structure, sliding a second pile segment on the strand until the second pile segment contacts an end of the first pile segment, and driving the second pile segment another desired distance into the earth. In this patent, the first pile segment has an end of the strand fixedly received therein. As the first pile segment is being driven into the earth, the strand will follow the first pile segment and extend outwardly therefrom. The second pile segment is then placed over the strand and driven along the strand until it comes into contact with the first pile segment.
U.S. Pat. No. 5,399,055, issued on Mar. 25, 1995, to E. T. Dutton, Jr. teaches a device and method to level and repair a failed concrete foundation. In this process, a series of cylindrical pile segments are jacked into the soil. Reinforcing steel is inserted into the fully installed stacked column of cylindrical pile segments and group is further pumped into the cylindrical pile segments to suitably fix the reinforcing steel to the inside of the cylindrical pile segments. This-forms a single shaft pile.
In these two types of pile systems, one utilizes a strand upon which segments are threaded, and the other requires the strand to be threaded into an installed stack of segments. The second method requires that the central conduit in the segment be rather large with respect to the cable. Even so, when a reinforcing strand is threaded into a pre-installed stack of blocks, there is no mechanism for aligning the blocks prior to installing the reinforcing strand. This method allows significant misalignments of the pile, such that in many cases the reinforcing strand is unable to travel the full depth of the pile. The resultant pile is deficient due to both the misalignment and the lack of full depth reinforcement. When such deficiencies exist, it would be necessary to start the process over again and reinstall the pile. As such, need has developed so as to assure the proper alignment between the pile segments during actual installation and provide continuous, full-depth reinforcement.
A problem with the process of U.S. Pat. No. 5,288,175 is that the end of the strand is anchored into a relatively small single pile segment prior to installation below the structure. Because of fabrication and handling costs, and because of the small amount of clearance between the structure and the earth, it is only possible to anchor the strand into a pile segment having a relatively small size. It is not feasible to use larger starter segments because of this small amount of clearance. If a greater clearance was made, then it would be possible to form a starter segment having a greater length and to transport such a large starter segment to the area beneath the structure. However, the weight of such an enlarged starter segment would make fabrication, transport and installation very difficult and costly. Mechanical devices would be required to properly transport the starter segment to the area. A starter segment having a length significantly greater than twelve inches would greatly increase the weight of the starter segment. The existing use of a single starter segment limits the strand anchoring capacity. As such, failure of the anchorage is possible. Also, this limited anchorage capacity may be inadequate for tensioning the strand upon completion. As such, with this prior art system of installing pile segments, buckling of the stacked pile segments is possible.
It is an object of the present invention to provide a process for installing pile segments which better resists misalignment of pile segments with respect to each other.
It is another object of the present invention to provide a process of installing piles which avoids the cost of manufacturing larger starter segments.
It is another object of the present invention to provide a process of installing piles which eliminates the difficulty of handling larger starter segments.
It is a further object of the present invention to provide a process of installing piles which provides greater strand anchorage capacity within the starter section.
It is still a further object of the present invention to provide a process for installing pile segments which is easy to use and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.
The present invention is a process for installing piles for supporting a structure upon the earth comprising the steps of: (1) driving a first pile segment into the earth a desired distance from the structure; (2) aligning a second pile segment upon the first pile segment such that a conduit in the second pile segment is axially aligned with a conduit of the first pile segment; (3) driving the first and second pile segments into the earth a desired distance from the structure; (4) affixing a strand into the conduits of the first and second pile segments so as to form a starter section; (5) sliding another pile segment along the strand so as to reside upon said starter section; and (6) driving the starter section and subsequent pile segments a desired distance from the structure.
The process of the present invention can further include the step of aligning a third pile segment upon the second pile segment such that the conduit of the third pile segment is axially aligned with the conduits of the first and second pile segments. The first, second and third pile segments are then driven into the earth a desired distance from the structure. The conduits of the first, second and third pile segments are holes which extend vertically through their respective segments.
In the process of the preferred embodiment of the present invention, the first pile segment is driven a desired distance into the earth from the structure. An alignment pin is then applied into the first pile segment such that a portion of the alignment pin extends outwardly of the top of the first pile segment. A second pile segment is then placed over the alignment pin such that a portion of the alignment pin extends outwardly of the top of the second pile segment. This allows the conduit of the second pile segment to be aligned with the conduit of the first pile segment. The alignment pin is then removed from the first and second pile segments. A strand is then affixed within the conduits of the first and second pile segments.
Alternatively, the step of aligning includes installing a tubular member into the conduit of the first pile segment such that a portion of the tubular member extends outwardly of a top of the first pile segment and then placing the conduit of the second pile segment over the tubular member.
Alternatively, the step of aligning includes the steps of installing a ring around an outer surface of the first pile segment so as to have a portion extending above a top of the first pile segment and placing the first pile segment into the ring such that a second pile segment is received in that portion of the ring. The step of affixing the strand includes bonding the strand within the conduits of the first and second pile segments. Specifically, a cementing material is injected into a space between the outer surface of the strand and a wall of the conduits of the first and second pile segments.
In the preferred method of the present invention, the step of sliding another pile segment includes sliding a plurality of pile segments along the strand so as to reside in stacked relationship upon the starter section. The strand extends through aligned conduits formed in the plurality of pile segments. A cap member is positioned between a portion of the structure and an uppermost pile segment of the plurality of pile segments. An end of the strand is anchored in the cap member.
The method of the present invention can also include removing a volume of earth from beneath a portion of the structure and then positioning the first pile segment directly below that portion of the structure.